1. Field of the Invention
The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a method for disposing a controller which controls a driver supplying a signal to pixel electrodes of a liquid crystal display device and a connection structure for the driver and the controller.
2. Description of the Related Art
An exemplary configuration for a conventional liquid crystal display device (LCD) will be described with respect to a TFT-LCD or an active matrix type LCD using a plurality of thin-film transistors (TFTs).
FIG. 1 is a plan view of a conventional liquid crystal display device as seen from above, while FIG. 2 is a cross-sectional view taken along the line 2-2' of the liquid crystal display device shown in FIG. 1.
As shown in FIG. 2, liquid crystal is sandwiched between a first insulating substrate 1 and a second insulating substrate 7 which are made of glass, quartz or the like. As shown in the magnified view on the left of FIG. 1: a pixel electrode 2, a TFT 4, a gate bus 5 for scanning the TFT 4, and a source bus 6 for supplying an image signal to the pixel electrode 2 via the TFT 4, are formed as a unit on the upper surface of the first insulating substrate 1 and a plurality of such units are arranged in matrix on the surface of the first insulating substrate 1.
The upper surface of the first insulating substrate 1 is opposed to the lower surface of the second insulating substrate 7 with a predetermined gap therebetween. A counter electrode 14 is formed on the lower surface of the second insulating substrate 7. A region in which the counter electrode 14 is formed and an image is displayed will be herein called a "screen region" 3. The first and the second insulating substrates 1 and 7 are adhered to each other via a seal member 8.
Around the screen region 3, a plurality of gate drivers 9 each supplying a scanning signal to the corresponding gate bus 5, and a plurality of data drivers 10 each supplying an image signal to the corresponding source bus 6, are provided. Each of these drivers 9 and 10 is mounted on a carrier tape 12 having two flexible electrode lines. One of the two flexible electrode lines is connected to a terminal of the gate bus 5 or a terminal of the source bus 6 via an anisotropic conductive film, while the other flexible electrode line is connected to a control circuit board 13.
A controller formed on the control circuit board 13 converts an image signal such as a video signal into an image signal which can be displayed on a liquid crystal display device. The image signal obtained by the conversion is output to the drivers 9 and 10 via the carrier tapes 12.
Various methods are used for mounting the drivers, for example:
(1) A method in which a carrier tape is used; PA1 (2) A chip-on-glass (COG) method in which an LSI chip for drivers is directly connected to the gate bus terminal or the source bus terminal of a liquid crystal display device; and PA1 (3) A monolithic method in which drivers and TFTs are formed on the same insulating substrate by utilizing a process for forming TFTs switching the respective pixels on the screen.
According to any of these methods (1) to (3), the drivers and the controller are required to be connected to each other. For connecting the drivers and the controller thereof, a method for connecting flexible electrode lines thereto with an anisotropic conductive film or solder or a method for connecting them by means of wire bonding is used, for example.
An exemplary monolithic method is described in Japanese Laid-Open Patent Publication No. 4-324826, in which a technology for reducing the area around the screen by superposing the drivers and a seal resin by the use of monolithic drivers is disclosed.
As an exemplary driver monolithic type liquid crystal display device, there is an active matrix type liquid crystal display device using polycrystalline silicon transistors. Since the mobility of a polycrystalline silicon driver is relatively high, it is possible to form a display section and a peripheral driver section on the same substrate.
Such a driver monolithic type liquid crystal display device has recently been put into practical use as a video view finder, a light valve for a liquid crystal projector or the like.
FIGS. 3 and 4 show a conventional driver monolithic type liquid crystal display device: FIG. 3 is a plan view of the driver monolithic type liquid crystal display device as seen from above, while FIG. 4 is a cross-sectional view taken along the line 4-4' of the liquid crystal display device shown in FIG. 3.
In this liquid crystal display device, two insulating substrates 1 and 7 for forming a liquid crystal panel are disposed so as to face each other via a predetermined gap therebetween. The insulating substrates 1 and 7 are connected via a seal member 8 provided around the peripheral portions thereof. Liquid crystal 15 is injected through an injection hole 22 into the space formed by the insulating substrates 1 and 7 and the seal member 8 and then sealed.
The liquid crystal display device shown in FIG. 3 is an active matrix type liquid crystal display device. On the upper surface of the first insulating substrate 1, a plurality of gate buses 5 and a plurality of source buses 6 are provided so as to cross each other and a plurality of TFTs 4 and a plurality of pixel electrodes 2 are formed in matrix.
The gate buses 5 are extended transversely through the seal member 8 to be connected to the output terminals of the gate drivers 9, while the source buses 6 are also extended transversely through the seal member 8 to be connected to the output terminals of the source drivers 10.
External input terminals 21 are provided on the surface of the first insulating substrate 1 so as to run from the drivers 9 and 10 towards the corresponding end faces of the substrate and are exposed thereon.
A counter electrode 14 is formed on the lower surface of the second insulating substrate 7. A plurality of pixel electrodes 2 are formed on the upper surface of the first insulating substrate 1 so as to face the counter electrode 14.
The external input terminals 21 formed on the upper surface of the first insulating substrate 1 are connected to the output terminals of external circuit boards 25 via film carrier tapes 24. In a conventional liquid crystal display device, the external circuit boards 25 on each of which a controller is mounted are connected to the corresponding drivers 9 and 10 by utilizing a TAB technology.
By downsizing a liquid crystal display device, a liquid crystal display device application product such as a computer or a word processor can also be downsized. It is particularly necessary to reduce the area of the peripheral portion around the screen of a liquid crystal display device which does not contribute to the display of an image.
However, in the above-described method in which a carrier tape having flexible electrode lines is used, if the connection area between the carrier tape and a driver or the connection area between the carrier tape and a controller is reduced, then a sufficient adhesion strength cannot be obtained therebetween. Therefore, a certain area is required for connecting the carrier tape to the driver or connecting the carrier tape to the controller and the area of the peripheral portion around the screen cannot be reduced without limit.